(For these Sand-wasps, cf. "The Hunting Wasps": chapters 13 and 18 to
20.--Translator's Note.)
My readers may differ in appraising the comparative value of the
trifling discoveries which entomology owes to my labours. The geologist,
the recorder of forms, will prefer the hypermetamorphosis of the
Oil-beetles (The chapter treating of this subject has not yet been
translated into English and will appear in a later volume.--Translator's
Note.), the development of the Anthrax (Cf. "The Life of the Fly":
chapter 2.--Translator's Note.) or larval dimorphism; the embryogenist,
searching into the mysteries of the egg, will have some esteem for my
enquiries into the egg-laying habits of the Osmia (Cf. "Bramble-bees and
Others": chapter 4.--Translator's Note.); the philosopher, racking his
brain over the nature of instinct, will award the palm to the operations
of the Hunting Wasps. I agree with the philosopher. Without hesitation,
I would abandon all the rest of my entomological baggage for this
discovery, which happens to be the earliest in date and that of which
I have the fondest memories. Nowhere do I find a more brilliant, more
lucid, more eloquent proof of the intuitive wisdom of instinct; nowhere
does the theory of evolution suffer a more obstinate check.
Darwin, a true judge, made no mistake about it. (Charles Robert Darwin,
born the 12th of February, 1809, at Shrewsbury, died at Down, in Kent,
on the 19th of April, 1882. For an account of certain experiments
which the author conducted on his behalf, cf. "The Mason-bees": chapter
4.--Translator's Note.) He greatly dreaded the problem of the instincts.
My first results in particular left him very anxious. If he had known
the tactics of the Hairy Ammophila, the Mantis-hunting Tachytes, the
Bee-eating Philanthus, the Calicurgi and other marauders, his anxiety,
I believe, would have ended in a frank admission that he was unable to
squeeze instinct into the mould of his formula. Alas, the philosopher of
Down quitted this world when the discussion, with experiments to support
it, had barely begun: a method superior to any argument! The little
that I had published at that time left him with still some hope of an
explanation. In his eyes, instinct was always an acquired habit. The
predatory Wasps killed their prey at first by stabbing it at random,
here and there, in the softest parts. By degrees they found the spot
where the sting was most effectual; and the habit once formed became a
true instinct. Transitions from one method of operation to the other,
intermediary changes, sufficed to bolster up these sweeping assertions.
In a letter of the 16th of April, 1881, he asks G.J. Romanes to consider
the problem:
"I do not know," he says "whether you will discuss in your book on the
mind of animals any of the more complex and wonderful instincts. It is
unsatisfactory work, as there can be no fossilised instincts, and the
sole guide is their state in other members of the same order, and mere
PROBABILITY.
"But if you do discuss any (and it will perhaps be expected of you), I
should think that you could not select a better case than that of
the sand-wasps which paralyse their prey as described by Fabre in his
wonderful paper in the 'Anales des sciences naturelles,' and since
amplified in his admirable 'Souvenirs...'"
I thank you, O illustrious master, for your eulogistic expressions,
proving the keen interest which you took in my studies of instinct, no
ungrateful task--far from it--when we tackle it as it should be tackled:
from the front, with the aid of facts, and not from the flank, with
the aid of arguments. Arguments are here out of place, if we wish to
maintain our position in the light. Besides, where would they lead us?
To evoking the instincts of bygone ages, which have not been preserved
by fossilization? Any such appeal to the dim and distant past is quite
unnecessary, if we wish for variations of instinct, leading by degrees,
according to you, from one instinct to another; the present world offers
us plenty.
Each operator has her particular method, her particular kind of game,
her particular points of attack and tricks of fence; but in the midst
of this variety of talents we observe, immutable and predominant, the
perfect accordance of the surgery with the victim's organization and the
larva's needs. The art of one will not explain the art of another,
no less exact in the delicacy of its rules. Each operator has her own
tactics, which tolerate no apprenticeship. The Ammophila, the Scolia,
the Philanthus and the others all tell us the same thing: none can
leave descendants if she be not from the outset the skilful paralyser or
slayer that she is to-day. The "almost" is impracticable when the future
of the race is at stake. What would have become of the first-born mammal
but for its perfect instinct of suckling?
And then, to suppose the impossible: a Wasp discovers by chance the
operative method which will be the saving attribute of her race. How are
we to admit that this fortuitous act, to which the mother has vouchsafed
no more attention than to her other less fortunate attempts, could leave
a profound trace behind it and be faithfully transmitted by heredity? Is
it not going beyond reason, going beyond the little that is known to
us as certain, if we grant to atavism this strange power, of which our
present world knows no instance? There is a good deal to be said for
this point of view, my revered master! But, once more, arguments are
here out of place; there is room only for facts, of which I will resume
the recital.
Hitherto I had but one means of studying the operative methods of the
spoilers: to surprise the Wasp in possession of her capture, to rob her
of her prey and immediately to give her in exchange a similar prey, but
a living one. This method of substitution is an excellent expedient. Its
only defect--a very grave one--is that it subjects observation to
very uncertain chances. There is little prospect of meeting the insect
dragging its victim along; and, in the second place, should good fortune
suddenly smile upon you, preoccupied as you are with other matters
you have not the substitute at hand. If we provide ourselves with the
necessary head of game in advance, the huntress is not there. We
avoid one reef to founder on another. Moreover, these unlooked for
observations, made sometimes on the public highway, the worst of
laboratories, are only half-satisfactory. In the case of swiftly-enacted
scenes, which it is not in our power to renew again and again until
perfect conviction is reached, we always fear lest we may not have seen
accurately, may not have seen everything.
A method which could be controlled at will would offer the best
guarantees, above all if employed at home, under comfortable conditions,
favourable to precision. I wished, therefore, to see my insects at work
on the actual table at which I am writing their history. Here very few
of their secrets would escape me. This wish of mine was an old one. As
a beginner, I made some experiments under glass with the Great Cerceris
(C. tuberculata) and the Yellow-winged Sphex. Neither of them responded
to my desires. The refusal of each to attack respectively her Cleonus or
her Cricket discouraged further progress in this direction. I was wrong
to abandon my attempts so soon. Now, very long afterwards, the idea
occurs to me to place under glass the Bee-eating Philanthus, whom I
sometimes surprise in the open engaged in forcing a bee to disgorge her
honey. The captive massacres her bees in such a spirited fashion that
the old hope revives stronger than ever. I contemplate reviewing all the
wielders of the stiletto and forcing each to reveal her tactics.
I was obliged to abate these ambitions considerably. I had some
successes and many more failures. I will tell you of the former. My
insect-cage is a spacious dome of wire-gauze resting on a bed of sand.
Here I keep in reserve the captives of my hunting-expeditions. I feed
them on honey, placed in little drops on spikes of lavender, on heads
of thistle, or field eryngo, or globe-thistle, according to the season.
Most of my prisoners do well on this diet and seem scarcely affected by
their internment; others pine away and die in two or three days.
These victims of despair nearly always throw me back, because of the
difficulty of obtaining the necessary prey at short notice.
Indeed it entails no small trouble to secure in the nick of time the
game demanded by the huntress who has recently fallen a captive to my
net. As assistant-purveyors I have a few small schoolboys, who, released
from the tedium of their declensions and conjugations, set out, on
leaving the classroom, to inspect the greenswards and beat the bushes
in the neighbourhood on my behalf. The gros sou, the penny-piece, if you
please, stimulates their zeal; but with misadventurous results! What I
need to-day is Crickets. The band sallies forth and returns with not a
single Cricket, but numbers of Ephippigers, for which I asked the day
before yesterday and which I no longer need, my Languedocian Sphex
being dead. General surprise at this sudden change of market. My young
scatterbrains find it hard to understand that the beast which was so
precious two days ago is now of no value whatever. When, owing to the
chances of my net, a renewed demand for the Ephippiger sets in, then
they will bring me the Cricket, the despised Cricket.
Such a trade could never hold out if now and again my speculators were
not encouraged by some success. At the moment when urgent necessity is
sending up prices, one of them brings me a magnificent Gad-fly intended
for the Bembex. For two hours, when the sun was at its height, he kept
watch on the threshing-floor hard by, waiting for the blood-sucker, in
order to catch him on the buttocks of the Mules which trot round and
round trampling the corn. This gallant fellow shall have his gros sou
and a slice of bread and jam as well. A second, no less fortunate, has
found a fat Spider, the Epeira, for whom my Pompili are waiting. To the
two sous of this fortunate youth I add a little picture for his missal.
Thus are my purveyors kept going; and, after all, their help would be
very inadequate if I did not take upon myself the main burden of these
wearisome quests.
Once in possession of the requisite prey, I transfer the huntress from
my warehouse, the wire-gauze cage, to a bell-glass varying in capacity
from one to three or four litres (1 3/4 to 5 or 7 pints.--Translator's
Note.), according to the size and habits of the combatants; I place the
victim in the arena; I expose the bell-glass to the direct rays of
the sun, without which condition the executioner as a rule declines to
operate; I arm myself with patience and await events.
We will begin with the Hairy Ammophila, my neighbour. Year after year,
when April comes, I see her in considerable numbers, very busy on the
paths in my enclosure. Until June I see her digging her burrows and
searching for the Grey Worm, to be placed in the meat-cellar. Her
tactics are the most complex that I know and more than any other
deserves to be thoroughly studied. To capture the cunning vivisector, to
release her and catch her again I find an easy matter for the best part
of a month; she works outside my door.
I have still to obtain the Grey Worm. This means a repetition of the
disappointments which I had before, when, to find a caterpillar, I was
obliged to watch the Ammophila while hunting and to be guided by her
hints, as the truffle-hunter is guided by the scent of his Dog. A
patient exploration of the harmas, one tuft of thyme after another, does
not give me a single worm. My rivals in this search are finding their
game at every moment; I cannot find it even once. Yet one more reason
for bowing to the superiority of the insect in the management of her
affairs. My band of schoolboys get to work in the surrounding fields.
Nothing, always nothing! I in my turn explore the outer world; and for
ten days the pursuit of a caterpillar torments me till I lose my power
of sleep. Then, at last, victory! At the foot of a sunny wall, under the
budding rosettes of the panicled centaury, I find a fair supply of the
precious Grey Worm or its equivalent.
Behold the worm and the Ammophila face to face beneath the bell-glass.
Usually the attack is prompt enough. The caterpillar is grabbed by the
neck with the mandibles, wide, curved pincers capable of embracing the
greater part of the living cylinder. The creature thus seized twists
and turns and sometimes, with a blow of its tail, sends the assailant
rolling to a distance. The latter is unconcerned and thrusts her sting
thrice in rapid succession into the thorax, beginning with the third
segment and ending with the first, where the weapon is driven home with
greater determination than elsewhere.
The caterpillar is then released. The Ammophila stamps on the ground;
with her quivering tarsi she taps the cardboard on which the bell-glass
stands; she lies down flat, drags herself along, gets up again, flattens
herself once more. The wings jerk convulsively. From time to time the
insect places its mandibles and forehead on the ground, then rears high
upon its hind-legs as though to turn head over heels. In all this I
see a manifestation of delight. We rub our hands when rejoicing at a
success; the Ammophila is celebrating her triumph over the monster in
her own fashion. During this fit of delirious joy, what is the wounded
caterpillar doing? It can no longer walk; but all the part behind the
thorax struggles violently, curling and uncurling when the Ammophila
sets a foot upon it. The mandibles open and shut menacingly.
SECOND ACT.--When the operation is resumed, the caterpillar is seized
by the back. From front to rear, in order, all the segments are stung on
the ventral surface, except the three operated on. All serious danger is
averted by the stabs of the first act; therefore, the Wasp is now able
to work upon her patient without the haste displayed at the outset.
Deliberately and methodically she drives in her lancet, withdraws it,
selects the spot, stabs it and begins again, passing from segment to
segment, taking care, each time, to lay hold of the back a little more
to the rear, in order to bring the segment to be paralysed within reach
of the needle. For the second time, the caterpillar is released. It
is absolutely inert, except the mandibles, which are still capable of
biting.
THIRD ACT.--The Ammophila clasps the paralysed victim between her legs;
with the hooks of her mandibles she seizes the back of its neck, at the
base of the first thoracic segment. For nearly ten minutes she munches
this weak spot, which lies close to the cerebral nerve-centres. The
pincers squeeze suddenly but at intervals and methodically, as though
the manipulator wished each time to judge of the effect produced; the
squeezes are repeated until I am tired of trying to count them. When
they cease, the caterpillar's mandibles are motionless. Then comes the
transportation of the carcase, a detail which is not relevant in this
place.
I have set forth the complete tragedy, as it is fairly often enacted,
but not always. The insect is not a machine, unvarying in the effect
of its mechanism; it is allowed a certain latitude, enabling it to
cope with the eventualities of the moment. Any one expecting to see
the incidents of the struggle unfolding themselves exactly as I have
described will risk disappointment. Special instances occur--they are
even numerous--which are more or less at variance with the general rule.
It will be well to mention the more important, in order to put future
observers on their guard.
Not infrequently the first act, that of paralysing the thorax, is
restricted to two thrusts of the sting instead of three, or even to one,
which is then delivered in the foremost segment. This, it would seem,
from the persistency with which the Ammophila inflicts it, is the most
important prick of all. Is it unreasonable to suppose that the operator,
when she begins by pricking the thorax, intends to subdue her capture
and to make it incapable of injuring her, or even of disturbing her when
the moment comes for the delicate and protracted surgery of the second
act? This idea seems to me highly admissible; and then, instead of three
dagger-thrusts, why not two only, why not merely one, if this would
suffice for the time being? The amount of vigour displayed by the
caterpillar must be taken into consideration. Be this as it may, the
segments spared in the first act are stabbed in the second. I have
sometimes even seen the three thoracic segments stung twice over: at
the beginning of the attack and again when the Wasp returned to her
vanquished prey.
The Ammophila's triumphant transports beside her wounded and writhing
victim are also subject to exceptions. Sometimes, without releasing
its prey for a moment, the insect proceeds from the thorax to the next
segments and completes its operation in a single spell. The joyous
entr'acte does not take place; the convulsive movements of the wings and
the acrobatic postures are suppressed.
The rule is paralysis of all the segments, however many, in regular
order from front to back, including even the anal segment if this boast
of legs. By a fairly frequent exception the last two or three segments
are spared. Another exception, but a very rare one, of which I have
observed only a single instance, consists in the inversion of the
dagger-thrusts of the second act, the thrusts being delivered from back
to front. The caterpillar is then seized by its hinder extremity; and
the Ammophila, progressing towards the head, stings in reverse order,
passing from the succeeding to the preceding segment, including the
thorax already stabbed. This reversal of the usual tactics I am inclined
to attribute to negligence on the insect's part. Negligence or not,
the inverted method has the same final result as the direct method: the
paralysis of all the segments.
Lastly, the compression of the neck by the mandibulary pincers, the
munching of the weak spot between the base of the skull and the first
segment of the thorax, is sometimes practised and sometimes neglected.
If the caterpillar's jaws open and threaten, the Ammophila stills them
by biting the neck; if they are already growing quiescent, she refrains.
Without being indispensable, this operation is useful at the moment of
carting the prey. The caterpillar, too heavy to be carried on the wing,
is dragged, head first, between the Ammophila's legs. If the mandibles
are working, the least clumsiness may render them dangerous to the
carrier, who is exposed to their bite without any means of defence.
Moreover, once on the way, thickets of grass are traversed in which
the Grey Worm can seize a blade and offer a desperate resistance to
the traction. Nor is this all. The Ammophila does not as a rule trouble
about her burrow, or at least does not complete it, until she has
caught her caterpillar. During the mining-operations, the game is laid
somewhere high up, out of reach of the Ants, on some tuft of grass, or
the twigs of a shrub, whither the huntress, from time to time, stopping
her well-sinking, hastens to see if her quarry is still there. For her
this is a means of refreshing her memory of the spot where she has laid
it, often at some distance from the burrow, and of preventing attempts
at robbery. When the moment comes for removing the game from its
hiding-place, the difficulty would be insurmountable were the worm,
gripping the shrub with all the might of its jaws, to anchor itself
there. Hence inertia of the powerful hooks, which are the paralysed
creature's sole means of resistance, becomes essential during the
carting. The Ammophila obtains it by compressing the cerebral ganglia,
by munching the neck. The inertia is temporary; it wears off sooner
or later; but by this time the carcase is in the cell and the egg,
prudently laid at a distance on the ventral surface of the worm, has
nothing to fear from the caterpillar's grapnels. No comparison is
permissible between the methodical squeezes of the Ammophila benumbing
the cephalic nerve-centres and the brutal manipulations of the
Philanthus emptying the crop of her Bee. The huntress of Grey Worms
induces a temporary torpor of the mandibles; the ravisher of Bees makes
them eject their honey. No one gifted with the least perspicacity will
confound the two operations.
For the moment we will not dwell any longer on the method of the
Hairy Ammophila; we will see instead how her kinswomen behave. After
protracted refusals the Sandy Ammophila (A. sabulosa, FAB.),on whom
I experimented in September, ended by accepting the proffered prey, a
powerful caterpillar as thick as a lead-pencil. The surgical method did
not differ from that employed by the Hairy Ammophila when operating on
her Grey Worm in one spell. All the segments, excepting the last three,
were stung from front to back, beginning with the prothorax. This single
success with a simplified method left me in ignorance of the accessory
manoeuvres, which I do not doubt must more or less closely recall those
of the preceding species.
I am all the more inclined to accept these secondary manoeuvres, not
as yet recorded--the transports of triumph and the compressions of the
neck--inasmuch as I see them practised upon the Looper caterpillars,
which differ so greatly from the others in external structure, exactly
as I have described them in the case of the Grey Worm, which is of the
ordinary form. Two species, the Silky Ammophila (A. holoserica,
FAB.) and Jules' Ammophila (See in the first volume of the "Souvenirs
entomologiques" what I mean by this denomination.--Author's Note.),
affect this curious prey, which moves with the stride of a pair of
compasses. The first, often renewed under glass during the greater part
of August, has always refused my offers; the second, her contemporary,
has, on the contrary, promptly accepted them.
I present Jules' Ammophila with a slender, brownish Looper which I
caught on the jasmine. The attack is not slow in coming. The caterpillar
is grabbed by the neck: lively contortions of the victim, which rolls
the aggressor over and drags her along, now uppermost, now undermost in
the struggle. First the thorax is stung, in its three rings, from
back to front. The sting lingers longest near the throat, in the first
segment. This done, the Ammophila releases her victim and proceeds
to stamp her tarsi, to polish her wings, to stretch herself. Again I
observe the acrobatic postures, the forehead touching the ground, the
hinder part of the body raised. This mimic triumph is the same as that
of the huntress of the Grey Worm. Then the Looper is once more seized.
Despite its contortions, which are not in the least abated by the three
wounds in the thorax, it is stung from front to back in each segment
still unwounded, no matter how many, whether supplied with legs or not.
I expected to see the sting refrain more or less in the long interval
which separates the true legs in front from the pro-legs at the back
(Fleshy legs found on the abdominal segments of caterpillars and certain
other larvae.--Translator's Note.): segments devoid of organs of defence
or locomotion did not seem to me to deserve conscientious surgery. I was
mistaken: not a segment of the Looper is spared, not even the last ones.
It is true that these, being eminently capable of catching hold with
their false legs, would be dangerous later were the Wasp to neglect
them.
I observe, however, that the lancet works more rapidly in the second
part of the operation than in the first, either because the caterpillar,
half subjugated by the triple wound at the outset, is easier to reach
with the sting, or because the segments more remote from the head are
rendered harmless with a smaller injection of poison. Nowhere do we see
repeated the care expended upon paralysing the thorax, still less the
insistent attention to the first segment. On returning to her Looper
after the entr'acte devoted to the joys of success, the Ammophila stabs
so swiftly that, on one occasion, I saw her obliged to begin all over
again. Lightly stung along its whole length, the victim still struggles.
Without hesitation, the operator unsheathes her scalpel for the second
time and operates on the Looper afresh, with the exception of the
thorax, which was already sufficiently anaesthetized. This done, all is
in order; there is no more movement.
After the stiletto the hooks of the mandibles rarely fail to intervene.
Long and curved, they nibble at the paralysed victim's neck, sometimes
from above, sometimes from below. It is a repetition of what the Hairy
Ammophila showed us: the same sudden squeezes of the pincers, with
rather long intervals between. These intervals, these measured bites and
the insect's watchful attitude have every appearance of telling us that
the operator is noting the effect produced before giving a fresh pinch
of the nippers.
It will be seen how valuable is the evidence of Jules' Ammophila:
it tells us that the immolaters of Looper caterpillars and those of
ordinary caterpillars follow precisely the same method; that victims
displaying very dissimilar external structure do not entail any
modification of the operative tactics so long as the internal
organization remains the same. The number, arrangement and degree of
mutual independence of the nerve-centres guide the sting; the anatomy of
the game, rather than its form, controls the huntress' tactics.
Let me mention, before I dismiss the subject, a superb example of this
marvellous anatomical discrimination. I once took from between the legs
of a Hairy Ammophila, which had just paralysed it, a caterpillar of
Dicranura vinula. What a strange capture compared with the ordinary
caterpillar! Bridling in thick folds beneath its pink neckerchief,
its fore-part raised in a sphinx-like attitude, its hinder-part slowly
waving two long caudal threads, the curious animal is no caterpillar
to the schoolboy who brings it to me, nor to the man who comes upon
it while cutting his bundle of osiers; but it is a caterpillar to the
Ammophila, who treats it accordingly. I explore the queer creature's
segments with the point of a needle. All are insensitive; all therefore
have been stung.